Pheromones Are Not Enough, Timing is Important Too

Traditionally, pheromones have been defined as substances that are secreted by insects in order to influence the behavior of insects of the same species, as opposed to allelochemicals — substances emitted by one insect species that influence the behavior of another species.

However, researchers from a University of Arizona-led team have found that many species of longhorned beetle use the same sex pheromone, which seems to contradict the generally accepted idea of one pheromone per species. Their research is described in an article in the Journal of Chemical Ecology.

So how do the different beetle species find suitable mates if they’re all attracted by the same pheromone? As the scientists found out, timing is everything.

“We found that beetles that produce the same pheromone are active at different times of day,” said lead author Robert F. Mitchell, a UA research associate in the department of neuroscience and the Center for Insect Science.

As part of his doctoral research at the University of Illinois at Urbana-Champaign, Mitchell studied the chemical attractants for dozens of species of longhorned beetles native to deciduous forests of eastern North America. The beetles bore into the woody stems of dead shrubs and trees.

He later focused on 11 species that were all attracted to the same chemical. When he and his colleagues put traps baited with that pheromone out in the woods, after 24 hours the traps contained “a big multi-species party.”

Initially, Mitchell and his colleagues were baffled. Such a multi-species party didn’t make sense, because mating outside one’s species doesn’t result in viable offspring.

“We asked, ‘How do they tell each other apart if they’re all producing the same thing?'” he said.

Senior author Lawrence M. Hanks learned about a rotating trap that could separate beetles by the time of day they entered the trap. That setup allowed the scientists to test whether different species were attracted only at certain times of day.

By using the rotating traps, the researchers found some species visited primarily in the daytime, some came in the early evening, and some came at night. Other experiments revealed that the 11 species also searched for mates at different times in the spring.

Once the team figured out that various beetle species sent out their scent signals during different parts of the year and at different times of the day, it all made sense.

“Our research provides a framework for understanding how insects that produce the same pheromone can produce separate signals,” Mitchell said.